Networks connecting a plurality of terminals (nodes) such as computers may have various topologies such as bus, star, ring and mesh topologies. An example of a bus network is Ethernet (registered trademark). Ethernet has a physical star topology but has a logical bus topology, in which each node can freely transmit a signal (data). On the other hand, a signal collision may occur in Ethernet, and in such a case, delivery of the signal is delayed (namely, latency is increased).
Like Ethernet, ring networks often are wired in a physical star topology in which each network node is connected to a central hub. An example of a ring network is Token Ring. In Token Ring, a signal called a “token” travels around a logical ring (token passing), and only a node where the token is present can send data. Namely, the nodes where the token is not present cannot send data, and therefore, collision of data on the network is prevented.
With regard to a communication system having a plurality of nodes connected to each other via Token Ring, it has been proposed to provide, as a flow control system to cope with a load variation at a receiver node without complicating the functions of the nodes, a system in which a sender node includes a send-out means that sends out a set of data addressed to a receiver node and a busy token and a relay means that, upon receipt of the set of data and token sent out by the sender node itself, sends out the set as it is, and a receiver node includes a relay means that, if there is no room to accept data when receiving the set of data and token, sends out the set as it is and an acceptance means that, if there is room to accept data when receiving the set of data and token, accepts the data included in the set (JP2001-326663A).